It is a prospective, randomized, double-blind, placebo controlled trial to assess the effect of 3 months treatment with sildenafil (20 mg/8 h), added to a pulmonary rehabilitation program, on exercise tolerance. Subjects: 60 patients (30 by treatment group). Main end-point variable: endurance time in constant work exercise test (CWET). Other measurements: 6 min walk distance, performance in incremental exercise test, physiological and metabolic response at iso-time and iso-load in CWET, dyspnea, and health-related quality of life.
